Differential transformers



April 2, 1968 J. CHASS 3,376,533

DIFFERENTIAL TRANSFORMERS Filed May 9, 1967 INVENTOR J'Acaa (If/ASS BY QIMIQ'WYM ATTORNEYS 3,376,533 Patented Apr. 2, 1968 3,376,533 DIFFERENTIAL TRANSFORMERS Jacob Chass, Forest Hills, N.Y., assignor to Pickering & Company, Inc., Plainview, N.Y., a corporation of New Yor Filed May 9, 1967, Ser. No. 637,151 5 Claims. (Cl. 336-136) ABSTRACT OF THE DISCLOSURE A non-symmetrical differential transformer having a null position at one end and an output voltage which is a linear function of the displacement of an armature core from the null position.

Background of the invention Differential transformers of the type composed of tubular bobbin of non-magnetic, non-conductive material and having primary and secondary coils wound thereon with a'displaceable magnetic armature core, the position of which determines the number and position of secondary coils magnetically coupled with the primary coil are well known. In transformers of this type secondary windings are frequently connected in series bucking relationship as well as series aiding relationship. By series bucking arrangement it is meant that the coils are connected so that when an AC current input is placed on the primary coils the output of one of the secondary coils is of an opposite phase to the output of the other secondary coil.

When the armature core of such a differential transformer is in a position where it magnetically links the primary with a combination of secondary coils providing a minimum or substantially zero output it is said that the null position has been achieved.

Constructions of such transformers wherein displacement of the armature in either direction from the null position results in an output voltage the amplitude of which is a function of the displacement distance irrespective of direction are known as symmetrical differential transformers whereas constructions having the null at one end providing an increase output voltage amplitude resulting from movement of the .armature in one direction only are known as non-symmetrical differential transformers. Certain advantages and benefits are achieved in non-symmetrical transformers as will appear by reference to United States Letters Patents 3,017,590 and 3,031,633.

The differential transformers shown in these patents have great utility, however, in the first the primary coils are sectioned and complicated secondary windings are provided, while in the second, which is much simpler in construction, the secondary windings are longitudinally displaced from the primary winding. There remains the need for a small, relatively high power output linear transformer in which the actual travel of the armature is short but highly effective and providing good resolution.

Summary of the invention A differential transformer comprising a tubular bobbin of a non-magnetic, non-conductive material having first and second secondary coils of electrically conductive wire wound around the bob-bin adjacent one another and connected together in bucking series arrangement, and having a primary coil of electrically conductive wire wound around the bobbin and over the length of the first and second' secondary coils with means insulating the secondary coils and the primary coils from one another, with each of the coils having a uniform number of turns with the density of turns of one of the secondary coils being greater than that of the other and an armature core movably disposed between the secondary coils and having a length greater than that of the secondary coil of lesser turn density and less than the length of the primary coil to permit the armature to extend across the entire length of the secondary coil of lesser turn density and a portion of the length of the remaining secondary coil in the null position with the secondary coils magnetically coupled to the primary coil through opposite ends of the armature core.

Description of the drawings In the accompanying drawings:

FIG. 1 is a longitudinal sectional view of the differential transformer of the present invention; and

FIG. 2 is a circuit diagram of the differential transformer of the present invention.

Description of the preferred embodiment A differential transformer constructed in accordance with the teachings of this invention is shown in the figures comprising an elongated primary coil 10 having a uniform number of turns per unit length, a first secondary oil 12 extending along a portion of the primary coil at one end thereof and having a uniform number of turns per unit length, a second secondary coil 14 extending along a portion of the primary coil adjacent the first secondary coil 12 and having a uniform number of turns per unit length, a third secondary coil 16 adjacent the primary coil and the end thereof adjacent coil 14 and having a uniform number of turns per unit length, and an armature core 18 of magnetic material movably disposed within the coils.

The second and third secondary coils 14 and 16, respectively, are connected in series aiding and this pair is connected with the first secondary coil 12 in series bucking arrangement. The number of turns and length of these coils are designed to provide an electrical balance or null when the core 18 is at the end of the assembly as indicated in the figures by the numeral 20 and an electrical voltage is applied between primary input terminals 22 and 24. When the core is displaced from this balanced or null point, an electrical output will appear between the secondary output terminals 26 and 28 which is a linear function of the displacement. The density of coil winding in coil 14 is greater than that of coil 12 so that in the null position of the armature and when the armature which is longer than the longitudinal distance of coil 12 but shorter than the longitudinal distance of coil 10 is linking all of the turns of coil 12 and a portion of the turns of coil 14 with a portion of the primary turns 10 the voltages induced in coils 12 and 14 will be of substantially equal amplitude. Since coils 12 and 14 are wound in series bucking relationship the voltages of equal amplitude will provide a null or substantially zero output.

In operation, when an input current is placed across primary coil 10 by the application of voltage between the terirr'nals 22 and 24, it will generate a magnetic flux which encircles through the core and the windings of coils 12 and 14 which are connected in opposition. The number of turns and length of these coils are designed to provide an electrical balance when the armature is at the end of the assembly indicated by the numeral 20. When the core is displaced away from the balance point, an electrical output will result which is a linear function of the displacement. Coil 16 is provided in order to extend the linear range of the transformer and is connected to coil 14 in an aiding configuration. Thus, there is provided a nonsymmetrical differential transformer which has its null position adjacent one end of the differential transformer and in which movement of the armature core from its null position toward the other end of the differential transformer provides an output current from the differential transformer since it will be linking the primary with a greater number of turns in coil 14 than 12 thereby providing the output.

Referring to FIG. 1, there is shown a preferred form of the diflerential transformer of the present invention.

The differential transformer comprises a tubular bobbin 30 formed of a non-magnetic, non-conductive material such as a plastic or ceramic. Bobbin 30 has a pair of radially extending end flanges 32 and 34 and a pair of radially extending additional flanges 36 and 38 spaced along the bobbin 30 between the end flanges. The flanges 32, 34 and 36 are of equal diameter and form two compartments. The flange 38 which lies between flanges 34 and 36 is of a decreased diameter and serves to section the compartment provided by flanges: 34 and 36.

The first secondary inductance coil 12 which is a helically wound coil of insulated electrically conductive wire is wound around the bobbin 30 within the compartment defined by flanges 34 and 38 and is of uniform; turn density throughout its length. Secondary coil 14 which is also a flanges 32 and 36 and this wire is also of an electrically conductive material which is insulated and is of uniform turn density.

The secondary coil 14 and 16 are connected in series aiding relationship and this combination is connected in 'buckingseries arrangement with coil 12. as shown diagrammatically in FIG. 2. The secondary coils are preferably made up of the same size wire so that they will expand or contract the same amount and will be stressed 'the same amount upon changes in temperature. Also the electrical resistance of the secondary windings will change the same upon changes in temperature so that the differential transformer is electrically stable.

Armature core 18 is movably disposed within the bobbin 30. Armature core 18 comprises a rod of magnetic material which is of a length greater than the longitudinal dimension of the secondary coil 12 but shorter than the total length of the winding 10. A sleeve 40 of a magnetic material is placed around the bobbin and discs 42 and 44 of a magnetic material are'pl'aced against the end flanges 32 and 34 to shieldthe coils and to reduce the reluctance ofthe magnetic flux path.

I claim:

1. A dilferential transformer comprising a tubular bobbin of a non-magnetic, non-conductive material, first and second secondary coils of electrically conductive wire each having a uniform number of turns per unit length wound around said bobbin adjacent one another and connected together in bucking series arrangement, a primary coil of electrically conductive wire wound around said bobbin and over the length of said first and second secondary coils, means insulating said first and second secondary coils and said second secondary coil having a greater density of turns than that of said first secondary coil, an armature core movably disposed between said secondary coils and having a length greater than that of said first secondary coil and less than that of said primary coil to permit the armature to extend across the entire length of said first secondary coil in the null position, and said secondary coils being magnetically coupled to said primary coil through opposite ends of said armature core.

2. A differential transformer in accordance with claim 1 in which the total length of said primary coil longitudinally along said bobbin is equal to the total length of the sum of the lengths of said secondary coils longitudinally along said bobbin. 7

3. A differential transformer in accordance with claim 1 in which said secondary coils are wound around-said bobbin between first and second flanges and separated from one another by a third flange and said primary coil is wound between said first and second flanges.

4. A differential transformer in accordance with claim 1 in which a third secondary winding is wound about said bobbin adjacent said primary coil and said second secondary coil and connected in series aiding arrangement with said second secondary coil to extend the linear range of said transformer.

5. A differential transformer in accordance with claim 3 in which a fourth flange of said bobbin 'is provided spaced from said second flange adjacent said primary coil and said second secondary coil and a third second-ary coil is wound about said bobbin between said second and said fourth flanges and connected in series aiding arrangement with said second secondary coil to extend the linear rangeof said transformer.

References Cited UNITED STATES PATENTS 3,017,589 1/1962 Chass 336-136 DARRELL L. CLAY, Primary Examiner. T. I. KOZMA, Assistant Examiner. 

